Translational control of Ybx1 expression regulates cardiac function in response to pressure overload in vivo.

RNA-protein interactions are central to cardiac function, but how activity of individual RNA-binding protein is regulated through signaling cascades in cardiomyocytes during heart failure development is largely unknown. The mechanistic target of rapamycin kinase is a central signaling hub that controls mRNA translation in cardiomyocytes; however, a direct link between mTOR signaling and RNA-binding proteins in the heart has not been established. Integrative transcriptome and translatome analysis revealed mTOR dependent translational upregulation of the RNA binding protein Ybx1 during early pathological remodeling independent of mRNA levels. Ybx1 is necessary for pathological cardiomyocyte growth by regulating protein synthesis. To identify the molecular mechanisms how Ybx1 regulates cellular growth and protein synthesis, we identified mRNAs bound to Ybx1. We discovered that eucaryotic elongation factor 2 (Eef2) mRNA is bound to Ybx1, and its translation is upregulated during cardiac hypertrophy dependent on Ybx1 expression. Eef2 itself is sufficient to drive pathological growth by increasing global protein translation. Finally, Ybx1 depletion in vivo preserved heart function during pathological cardiac hypertrophy. Thus, activation of mTORC1 links pathological signaling cascades to altered gene expression regulation by activation of Ybx1 which in turn promotes translation through increased expression of Eef2.